In the formation of integrated circuits on the surface of a semiconductor substrate, oxynitride films are frequently grown or deposited over the surface of a crystalline substrate such as silicon. Oxynitride films may have superior electrical properties, including high electron mobility and low electron trap density that are desirable for device operation in semiconductor applications. Advantages of nitrogen incorporation in a thin oxide film include: reduced boron penetration through a p-doped polysilicon gate, improved interfacial smoothness, increased in the dielectric constant of the oxynitride film, and improved barrier properties to prevent diffusion of metal oxides or metal gate materials into the underlying substrate. Several methods have been developed for forming oxynitride films for semiconductor applications and, following formation of these films on a substrate, oxynitride films are frequently annealed to further improve their material and electrical properties.
The ability to incorporate nitrogen during processing is of critical importance for device performance. In one example, a thin oxide film may be annealed in the presence of a nitrogen-containing gas, such as nitrous oxide (N2O), ammonia (NH3), nitric oxide (NO), and thermal and plasma nitrogen (N2), at predetermined processing conditions to form an oxynitride film by nitrogen incorporation from the gas into the oxide film. However, one serious shortcoming associated with using current nitrogen sources is variability in nitrogen incorporation and difficulty in preventing nitrogen penetration into the substrate. Both of these shortcomings deteriorate performance of the resulting MOSFET. Other problems include unacceptable oxynitride thickness variations and variation in nitrogen concentration in the oxynitride films. In other words, current processing techniques result in batch to batch variability, which directly impacts the overall quality of the oxynitride film and any semiconductor device constructed with the oxynitride film.
There is thus a need for new methods that provide high nitrogen incorporation at controlled depths while providing a controlled rate of oxide growth. Also, what is needed is improved reliability of nitrogen incorporation and tailoring the concentration and location of nitrogen within the oxide film.